About this session:
The rate and extent of starch digestion in the rumen depends on a myriad of complex interactions among rumen microorganisms, kernel structure and the degree and method of grain processing. Regardless of grain type the high degree of lignification and presence of a waxy cuticle makes the hull a formidable barrier to microbial digestion in the rumen. In order for ruminal starch digestion to proceed, this barrier must be breached either via processing (i.e., grinding, rolling, steam flaking) or mastication so as to expose the endosperm and the starch it contains to ruminal microorganisms.
Exposed starch granules are readily digested by amylolytic members of the rumen microbial population, with bacteria and protozoa being responsible for the majority of starch digestion in the rumen. However, starch granules that are tightly embedded within the vitreous protein matrix can be sheltered from microbial attack and it is these starch granules that account for the majority of by-pass starch in corn and sorghum grain diets.
This is seldom a problem with barley grain based diets, provided that they are properly processed. Once free of the protein matrix, there is little difference in the ability of rumen microbes to digest starch granules from different grain types. This likely reflects the myriad of amylases produced by the diversity of microbes that are capable of digesting starch.
Recent work in our lab suggests that only a fraction of the amylolytic and proteolytic ruminal bacteria involved in starch digestion have been identified. Further identification and characterization of the role of these unknown ruminal bacteria in starch digestion could provide new insight into the mechanisms of ruminal starch digestion.
Enhanced digestion of starch in the rumen often results in improved growth and feed efficiency as by-pass starch often results in a decline in total tract starch digestibility as reflected by an increase in the concentration of starch in faeces.
The development of rapid analysis procedures such as near infrared analysis of starch in feces could provide insight into management practices that further improve ruminal starch digestion and consequently the feed value barley grain to improve the overall productivity of the ruminant host.